1. Field of the Invention
The present invention relates to an exposure apparatus that includes an illumination optical system for illuminating an original and a projection optical system for projecting light from the original onto a substrate, and exposes the substrate to light through the original and the projection optical system while the original and the substrate are being scanned in a direction perpendicular to an optical axis of the projection optical system.
2. Description of the Related Art
For manufacturing semiconductor devices, such as a semiconductor memory formed of an extremely fine pattern, using a photo-lithography technique, a circuit pattern depicted on a reticle is projected on a wafer by a reduction projection optical system to form the circuit pattern. By the demand for further miniaturizing the pattern of the semiconductor device, the exposure apparatus has been responded to the miniaturizing simultaneously with the development of a resist process. A means for improving resolution of the exposure apparatus includes a method for increasing the numerical aperture (NA) of the projection optical system and a method for reducing the exposure wavelength.
As a method for increasing the numerical aperture (NA) of the projection optical system, the liquid immersion has been recently developed for approaches toward the higher NA. It is generally known that the resolving power is proportional to the wavelength of exposure light and is inversely proportional to the NA. The minimal resolution of transferring by a reduction projection exposure apparatus is also proportional to the wavelength of exposure light, and the resolution increases with decreasing wavelength. Hence, along with needs for miniaturization of semiconductor devices, ArF excimer laser with an oscillation wavelength of about 193 nm has recently been in the mainstream instead of KrF excimer laser with a wavelength of 248 nm, and the development of EUV (extreme ultraviolet radiation) with a further shorter wavelength has been in progress.
One reason for reduction in resolution includes every linewidth error that firstly includes the lengthwise/crosswise linewidth error. For correcting the error, an HV (high voltage) correction filter may be used. Then, for correcting the linewidth error every shot, the linewidth error every shot is reduced by controlling the fundamental pulse number of laser for every shot, i.e., the exposure light quantity. The linewidth error in a scanning direction within a shot is reduced by controlling the pulse number of laser within a shot.
For the linewidth error in a non-scanning direction within a shot, filters with different densities are arranged on either side of the optical axis, respectively, in the vicinity of a primary image plane so as to inside direct the lower density portion. Then, by driving the filters in directions opposite to each other so as to change the light quantity in the center and the vicinity of transmitting rays, the exposure light quantity is corrected (see Japanese Patent Laid-Open No. 2002-033272, for example).
In the conventional above-example, for the linewidth error in the non-scanning direction within a shot, the filters with different densities are arranged on either side of the optical axis, respectively, in the vicinity of a primary image plane so as to inside direct the lower density portion. Then, by driving the filters in directions opposite to each other so as to change the light quantity in the center and the vicinity of the transmitting rays, the exposure light quantity is corrected. However, because the optical filter is used, the transmitting light quantity is reduced by about 10%. In the vicinity of the primary image plane, a travel masking blade mechanism and a slit-shape correction mechanism are arranged for scanning exposure. Therefore, in practice, an intermediate imaging plane must be further arranged in optical conjugation with this plane so as to therefore correct the exposure light quantity. Thus, there has been a weak point that the light path length of the illumination optical system is increased to also increase the number of optical devices.